Resistance furnace



' G. S. PETERSON RESISTANCE FURNACE Dec. 1, 1931.

2 Sheets-Sheet 1 Filed April 15, 1930 v aw N\ Nu x3 &

R. m mn E M W W Mr rm M a? Dec. 1, 1931. s PETERSON 1,834,640

RESISTANCE FURNACE Filed April 15, 1930 2 Sheets-Sheet 2 B. T l 2R0}INVENTOR.

Guy 5;. Peterson A TTORNEYJ Patented Dec. 1, 1931 UNITED STATES PATENT.OFFICE GUY B. PETERSON, 0] EAST CLEVELAND, OHIO, LSSIGHOB T0 In STRONG,caausu: LID EAIIOHD COMPANY, 01' CLEVELLHILOHIO, A CORPORATION 01' OHIOnnsrsranca roaaacn My invention relates to electric furnaces ofresistance type which are intended for use in heat treatin processeswherein the work must be quickly raised to a high temrature, but withoutmelting any part beore it is all heated throu h. To this end certain ofthe resistance e ements must be,

' capable of quickly generating great heat,

. and thereforeone ofthe aims ofj'my invenution is to so arrange thefurnace elements that the work will not be directly exposed to surgesofheat from the resistors. Another aim is the provision of circuits,controla, and a mode of operation such that the ll reqmsite temperaturesare very rapidly at- "particularly pointed out in the claims.

The annexed drawings and the following description set forth in detailcertain me'cha-.

' nism embodying the invention, such discloud means constituting,however, but one 80 of various mechanical forms in which the principleof the invention may be used.

In said annexed drawings:

Fig. 1 is a transverse cross section .on the I line 1- 1 of Fig. 2; Fig.2 is a longitudinal 8! cross section on the line 2-2 of Fig. 1,; and

Figs."3 and 4 are diagrams of'possible circuits. a

Referring particularly to Fig. 1, my furnace is of commercial type inits general.

form, comprising a heating chamber 1, lined with refractory material, 2,which is again surrounded by the usual insulation 3, externally cased asat 4, the whole assembly being supported, in the smaller sizes, on asuitable stand 5. Access to the heating chamber is bad by a passage 6,closed by a door here shown as including an inner refractory tile 7 andan outer insulating section 8, the whole assembly resting on a shelf 9and movable on 6 guides 10. A peep hole 11 allows the work Applicationfled April 15,

mo. Serial 1.. 444,429.

to be watched. A suitable rack 12 within the chamber 1 supports aremovable work-holding muiiie 13, here shown as a tra made of a suitableheat-resisting materia such as carborundum, and having a flat bottom Itand relatively low sides 15 The mufile 13' is held in place by aremovable tile 16.

Resistors 21, 22 and 23 are arranged upon suitable holders 24 within theheating chamber 1, and are connected in their circuits by water-cooledconductors, such as 25. The. resistors are here shown as grouped inpairs 'the grouping, however, being a matter of convenience. In the typeof furnace illustrated, the resistors are of carbon silicide, but othermaterials ca able ofoarryin high current densities, wo d be suitable. twill be particularly noted that the resistors are so placed relativelyto the muflie 13 that some part of the mufiie will always be betweenthework in the muflle and each resistor, or in other words, that thebottom and sides 15 of the mufiie always act to screen oif directradiation of heat to the work. For this urpose the top of the mufiieside 15 is ma e as high as the top of the upper resistor bar of eachside pair 21 and 22, it being understood that the work will be keptbelow the to of the side 15. The reason for this has n suggested in thestatement of invention, and will be further explained below. Anelectrical system for the furnace is shown in a transverse diagrammaticview in Fig. 3. The resistors 21 and 22 at the sides of the furnace areconnected in series on a single circuit, parts of which are shown insolid lines and part dotted to indicate connections on the front andrear ends, respectively,

of the resistors. Current for the circuit s supplied from the line 23and iscut on and ofl by suitable thermally responsive instruments. Suchinstruments may conveniently comprise a thermocou le T appropriatelylocated in the heating c amber and connected to a pyrometer controllerP, which in turn actuates a controller anel C between the resistors21,22 and the line 23. The resistors 24 under the muflle are on theirown separate circuit supplied from another line 25. This circuitincludes a cut-off S which will ordinari- 1y be manual only, although itmay be ther mally governed, ut within a different tem-' perature rangefrom the pgrometer setting as will be apparent from t e description ofthe operation, below.

other arrangement of the resistor circuits is shown diagrammatically inFig. 4, wherein the constant circuit includesonly the two top resistors31, and the remaining four, 32, 33, are automatically controlled For theforms shown in Figs. 3 and 4,'hav1ng all resistors of the same size andconnected in series, and using two-wire supply systems, the supply forthe four-resistor circuit may convenlently be 220 volts, and that forthe tworesistor circuit, 110 volts. 'The circuit details are, of course,subject to modification accordin to the characteristics of theresistors, of t e current, and so on. A series arrangement of theresistors is illustrated in Fi 3 and 4, but it will be understood that,It ough this is a convenient showing, the exact hook-up of the resistorsis sub'ect to variation as desired, within the limits of the invention.

In 0 ration, the resistors in the circuit controlle by the switch S (24in Fig. 3; 31 in Fig. 4 are all kept on constantly and are designe andrun so as to keep the heat of the furnace not quite up to the requiredworking temperature. For example, if a workin temperature of 2450 F.should be require the bottom resistors would be relied on to supply theheat to keep the chamber 1 up to about 2400", and the resistors incircuit with the panel C (21, 22, Fig. 3; 32, 33, Fig. 4) to bring it upquickly to 2450 F., after 0 enin the door and introducing new wor hacooled it down somewhat. The temperature of the constantly-operatedresistors is, of course related to the character of the work.

In' the treatment of high-speed steel articles, the temperatures are onthe order of 2000 F. to 2450 F., the work must be brought up to themaximum temperature within a few seconds, but without allowing the edgesto melt before the thicker parts are heated throu h. Even though thework is preheated be ore loading it into the furnace, the opening of thedoor and the introduction of the work will lower the heating chambertemperhaps The control system p erature, P, C, will then operate to cutin the adtherefore give a 0 screened from the direct action of ditionalresistors, which are capable of operating at a high current density,such as 80 watts per square inch of surface, and which surge of heatwhich would melt the edges of the tools before the thicker parts couldheat up, except that the work is this surge by the mufile walls 12.

While I have shown and described an embodiment of my invention designedfor temperature ranges above the reach of metallic resistors, it will beapparent that theprinciheat surge or direct ra ation from the resistors.

It will therefore be understood that I do not limitm self to the form ofthe invention above described, but that it may be embodied in any mannerwithin the scope and spirit of the ap nded claims.

What claim is:

1. In an electrical furnace, an open-top d work-receiving muflle havingupstandiiig sides, a group of resistors therebeneath, a group ofresistors therealongside, the sides of the muflie extending at least ashigh as the top portion of the side resistors.

electric resistance furnace comprising, in combination, an open-toppedmuflie, a bottomand upstandin sides on said muffle, said bottom and 'sides defining a workholding space, a pluralit of heating elements m saidfurnace so d isposed that some portion of the mulfle is interposedbetween every heating element and the work-holding space, and means forindependently regulating various of the said heating elements.

3. An electric resistance furnace including in combination, a mufiiepartly open within said furnace, a plurality of resistors adjacent saidmuflie,

work in said muflle, two electrical circuits in said furnace eachincluding certain. of said resistors, and independent control means foreach circuit. p 4. An electric resistance furnace incombination, amuilie partly open within said furnace, a plurality of resistorsadjacent said muflle, elements of said mufile directly interposedbetween'said resistors and work in said'mufile, two electrical circuitsin said furnace each including certain of said res1stors,inde ndentcontrol means for each circuit, one 0 said control means being re-'sponsive to narrow thermal changes.

5. In an electrical furnace, an open-top d work-receiving mufile havingupstanding s1des, a group of resistors therebeneath, a group ofresistors therealongside, the sides of the mufile extending at least ashigh as the top portion of the side resistors, and separate controlmeans for each of said groups.

6. In an electrical furnace, an open-topped work-receiving mufile havingupstanding sides, a group of resistors therebeneath, a group ofresistors therealongside, the. sides elements of said mufile; directlyinterposed between said resistors and including,

of the muflle extending at least as high as the top portion of the sideresistors, separate control meansfor each of said grou s, the controlmeans for the side groups being thermoresponsive.

7. In an electrical furnace, an open-topped work-receiving muflie havingupstanding sides, a group of resistors therebeneath, a group ofresistors therealongside, the sides of the mufile extendin at least ashigh as the to portion of the sig ca circuit including a thermostat andsaid side groups of reslstors, another electrical circuit including thebottom 'group of resistors. w

' 8. An electric furnace comgirising a WOI'k'. receiving space, aplurality o resistors thereabout, a circuit including certain of saidresisters and means for intermittently switch- Y ing said certainresistors on or oil, screening means between said certain resistors andsaid said container constituting a screen between work-receiving space.

9. An electric furnace comprising a p1u-' rality of resistors, saidresistors being divide'd into groups, one of said groups being adaptedfor relatively constant and the other for relatively intermittentoperation, a container adapted to hold work in said furnace,

said intermittently operated resistors and the work.

10. A method of operating a resistance furnace which comprisesinterposing a screen between the resistors and work in the 'furnace, andoperating said resistors in groups, using one group to give a constantsupply of heat slightly below the required temperature,

and the other to give intermittent additional heat to the requiredtemperature.

11. A method of operating a-resistance furnace which comprises operatingsaid in groups, using one group to give a constant supply of heatslightly below the required" temperature, and the other to giveintermite resistors, an electribars and the work-holding space of saidhearth.

14. An electric resistance-furnace includ-- our s. PET 0N.

tent additional heat to the required temperav ture, and interposing ascreen between the intermittently operated resistors and work in thefurnace.

12. An electric resistance furnace including, in combination, a mufllewithin said furnace, a plurality of resistors adjacent said muflle,elements of said mufile directly inter- I posed between said resistorsand work in said muflie, a plurality of electrical circuits in saidfurnace each including certain of said resistors, and pyrometer controlmeans in certain of said circuits.

13. An electric resistance furnace includ- Signed byme tliis llth day ofA ril, 1930. i

ing, in combination, a hearth, a plurality of I resistor bars arrangedparallel to said hearth, certain of said resistor bars being adapted forconstant operation and the others for intermittent operation and screenmeans be, tween said intermittently operable resistor

